Nvidia had an electrical problem with the early batch of 8600 GTS. This is now history and Nvidia replaced the damaged part on all of the boards.
This won't affect the launch at all. The issue was a nasty one. It would shut down your PC after benchmarking for a while. The component is changed and Nvidia partners are getting new cards with the replaced part.
This is nothing that should concern the end users as the cards you buy after 17th will be completely trouble free at least when it comes to this issue.
We believe that Geforce 8600 will be a very successful unit and Nvidia has high hopes for this DirectX 10 chip.